Conventional circuits have been used to control a rate of ramping a control voltage applied to a gate node of a control switch (sometimes referred to as a high side switch) in a synchronous buck converter. FIG. 1 is an example diagram of a voltage ramping circuit to ramp a switch control voltage according to the prior art.
In general, as shown in FIG. 1, the conventional voltage ramping circuit 185 in power supply circuit 170 includes a slow charging path and a fast charging path to charge a respective gate node 198 of control switch 171. As known in the art of power supplies, the control switch 171 is activated subsequent to deactivating the synchronous switch 172. More specifically, following deactivation of synchronous switch 171, the voltage ramping circuit 185 activates switch 190 to activate a slow charging path through a combination of capacitor 180 and resistor 175.
When activated, the slow charging path charges the gate node 198 of control switch 171. After a predetermined amount of time of activating the slow path and at least partially charging the voltage of gate node 198, the delay circuit 199 additionally activates switch 192 to charge the gate node 198 of control switch 171 at a faster charging rate (using the fast path).
Thus, according to the conventional ramping circuit 185, during a first portion of time when only the slow path through resistor 175 charges the gate node 198 via activation of switch 190, the voltage at gate node 198 of control switch 110 charges according to a first rate dictated by a combination of the capacitor 180 and the resistor 175. During a second time segment, subsequent to activation of switch 190, the delay circuit 199 activates switch 192, producing a faster path for charging the gate node 198. The fast path bypasses the slow path including the resistor 175, effectively coupling the voltage from capacitor 180 directly to the gate node of control switch 171, more quickly increasing the voltage applied to the gate node 198.